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Monoamine oxidase content in extracts of human blood platelets was determined independently of MAO activity measurements with a recently developed monoclonal antibody against human platelet monoamine oxidase (MAO B) in a competitive radioimmunoassay. Administration of a single oral dose of the irreversible inhibitor tranylcypromine to normal human subjects resulted in a rapid and marked inhibition of platelet MAO catalytic activity within 1 day, followed by recovery of activity to normal levels within 2 weeks. In contrast, there was no change in the net concentration of MAO protein during this time. Since recovery of MAO B activity approximated the reported half-life of blood platelets, these results suggest that recovery of platelet MAO activity after tranylcypromine treatment is due to the replacement of old platelets by new ones which contain catalytically active MAO B.

In the previous model of a thalamic neuron (R. M. Rose & J. L. Hindmarsh, Proc. R. Soc. Lond . B 237, 267-288 (1989)), which we referred to as the z -model, the burst response was terminated by the slow activation of a subthreshold outward current. In this paper we show that similar results can be obtained if the burst response is terminated by slow inactivation of the subthreshold inward current, I s a . We illustrate the use of this new model, which we refer to as the h a -model, by using it to explain the response of a thalamic neuron to a double ramp current. The main aim of the paper is to show how the stability and state diagrams introduced previously can be used to explain various types of firing pattern of thalamic and other neurons. We show that increasing the threshold for the fast action potentials leads to low threshold spikes of increased amplitude. Also, addition of a second subthreshold inward current adds a new stability region, which enables us to explain the origin of plateau potentials. In addition, various types of subthreshold oscillation are produced by relocating a previously stable equilibrium point in an unstable region. Finally, we predict a sequence of responses to current steps from different levels of background current that extends the burst, rest, tonic sequence of thalamic neurons. The stability and state diagrams therefore provide us with a useful way of explaining further properties of thalamic neurons and appear to have further applications to other mammalian neurons.

The static friction, or "stiction-friction", in McKee-Farrar and Charnley-Müller prostheses in a hip joint simulator was compared with dynamic friction determined while the prostheses were oscillated. Under physiological conditions stiction-friction differed little from dynamic friction in both metal-on-metal and metal-on-plastic prostheses, and was affected very little by the lubricant as long as some fluid was present. Stiction-friction increased significantly only after relatively long stationary periods and high loads. However, the frictional forces generated in total hip-replacement prostheses were at least forty times higher than those generated in normal joints and may well be enough to cause late loosening of acetabular components by fatigue failure.

We have previously discussed qualitative models for bursting and thalamic neurons that were obtained by modifying a simple two-dimensional model for repetitive firing. In this paper we report the results of making a similar sequence of modifications to a more elaborate six-dimensional model of repetitive firing which is based on the Hodgkin-Huxley equations. To do this we first reduce the six-dimensional model to a two-dimensional model that resembles our original two-dimensional qualitative model. This is achieved by defining a new variable, which we call q. We then add a subthreshold inward current and a subthreshold outward current having a variable, z, that changes slowly. This gives a three-dimensional (v,q,z) model of the Hodgkin-Huxley type, which we refer to as the z-model. Depending on the choice of parameter values this model resembles our previous models of bursting and thalamic neurons. At each stage in the development of these models we return to the corresponding seven-dimensional model to confirm that we can obtain similar solutions by using the complete system of equations. The analysis of the three-dimensional model involves a state diagram and a stability diagram. The state diagram shows the projection of the phase path from v,q,z space into the v,z plane, together with the projections of the curves z = 0 and v = q = 0. The stability of the points on the curve v = q = 0, which we call the v, q nullcurve, is determined by the stability diagram. Taken together the state and stability diagrams show how to assemble the ionic currents to produce a given firing pattern.

In order to study the temporal sequence of radiographic, histological, mechanical, bacteriological, and chemical changes around the femoral component following total hip replacement, a model was created by implanting plastic-on-metal total hip replacements in sheep and walking the animals on a concrete surface beginning six weeks postoperatively. This model demonstrated a decreased torsional rigidity between the prosthesis and the femoral cortex in all sheep. Failure of bonding occurred at the bone-cement interface and appears from our results to be most probably due to alterations in the functional stress of the proximal end of the femur following insertion of the femoral component rather than exothermic polymerization, toxicity of free monomer residue, or infection.An understanding of the causes of loosening of cemented metal femoral components in total hip replacement has been thwarted by a lack of specimens at sequential times in the loosening process. Since a patient is not operated on until the prosthetic components are completely loose, such specimens are difficult to obtain clinically. For this reason a model for examining the bone-cement interface, measured by decreased torsional rigidity of the prosthesis relative to the bone, was developed in sheep. Of all the parameters studied, those inherent in the effects (mechanical or vascular, or both) of insertion of the prosthesis itself appeared to be the most likely cause of the change in the mechanical properties of the interface. This suggests that degenerative changes of the bone-cement interface may be inevitable.

Scanning electron microscope examination of the polyethylene components of 8 total hip and 16 total knee prostheses which had been implanted 4--96 months revealed that in many cases severe wear may not necessarily be caused by the presence of acrylic cement debris or other abrasives. The craters and cracks observed on severely worn surfaces are associated with fusion defects in the plastic itself. The fusion defects were seen to occur as a result of the low temperature necessary to mold ultrahigh molecular weight polyethylene and are (at least at present) difficult to avoid. As a consequence of the above and variability of molecular weight in this material, relatively wide variations in wear rate should be expected even in the absence of acrylic debris.

Pneumonitis was produced in CD-1 mice by intratracheal instillation of murine cytomegalovirus. Lethal pneumonia occurred after instillation of virus derived from partially purified salivary gland homogenates, whereas virus attenuated by serial passage in cell culture caused mild disease and no mortality, even though both virulent and attenuated strains achieved comparable peak titers in lung homogenates. Virulence was characterized by rapid association of virus with pulmonary macrophages and early spread of virus from macrophages to susceptible parenchymal cells. This resulted in enhanced viral growth and cellular destruction during the first 5 days of infection. Delay in the early growth of murine cytomegalovirus in pulmonary parenchyma may diminish the destructive effects of virus on the lung and prevent mortality.

The studies reported here focus on the relation of nitrogen dioxide exposure to susceptibility to viral respiratory infection in a murine model of pneumonia, created by intratracheal inoculation of an endogenous murine pathogen, mouse cytomegalovirus. The purpose of this work is to clarify the potential role of nitrogen dioxide exposure in the pathogenesis of viral infection of the lower respiratory tract. Previous human epidemiologic studies have presented conflicting information about the relationship of nitrogen dioxide to acute, self-limited episodes of respiratory illness, which are characteristic of viral respiratory infection. Some studies have found an association between exposure to elevated ambient levels of nitrogen dioxide and increased occurrence of acute respiratory illness. In one study this association was found to be strongest in children in the first two years of life. However, other epidemiologic studies have failed to observe this relation. To determine if there is scientific evidence for the possible relation of nitrogen dioxide exposure to human respiratory infection, our studies were performed to assess the impact of nitrogen dioxide on respiratory tract susceptibility to initial, or primary, infection, as well as to recurrent infection, or reinfection, with the identical virus. The latter mechanism of viral respiratory infection is of particular interest, since reinfection is a common method for the development of infection of the lower respiratory tract during early childhood. Outbred CD-1 mice were exposed to either air or nitrogen dioxide for six hours a day on two consecutive days prior to inoculation with murine cytomegalovirus, and then were reexposed to the same level of nitrogen dioxide for six hours a day on four consecutive days, beginning the day after viral inoculation. Susceptibility to primary infection was determined by inoculating animals with an amount of virus (10(2) plaque-forming units) that is too small to produce viral infection in the lungs of normal animals. Mice exposed to 5 parts per million (ppm) nitrogen dioxide routinely developed viral replication in the lung and histologic evidence of pneumonitis after inoculation with this amount of virus, whereas air-exposed animals did not. Most importantly, animals exposed to 5 ppm nitrogen dioxide could be infected with a viral inoculum that was 100-fold smaller than that required to consistently produce viral infection in air-exposed mice. Enhanced susceptibility to infection was found after exposure to 5 ppm nitrogen dioxide, but was not observed with exposure to 2.5 or 1 ppm nitrogen dioxide.(ABSTRACT TRUNCATED AT 400 WORDS)

Based on experience with three cases of endobronchial non-Hodgkin's lymphoma and a review of cases previously reported, two patterns of lymphomatous involvement of airways are described. The Type 1 pattern is characterized by diffuse submucosal infiltrates occurring in the presence of intra- and extrathoracic lymphoma. In Type 2 cases, central airways are involved by a solitary mass in the absence of clinically apparent systemic lymphoma. The clinical-radiologic picture is characterized by signs of pneumonitis in Type 1 cases, while in Type 2 cases, signs of airway obstruction uniformly occur.

Guinea pigs were inoculated by the respiratory route with wild-type (Cyr) or vaccine (Oka) strain varicella zoster virus (VZV). Wild-type cell-free virus obtained by sonication produced neutralizing antibody responses in steroid-treated animals when given via the intratracheal route, and induced neutralizing antibody as well as a pneumonitis in normal animals when given via the intrabronchial (i. b.) route. A humoral response also followed i.b. instillation of cell-associated wild-type or vaccine strain VZV. Prior i.b. administration of thioglycollate or exposure to hyperoxia altered the number and function of pulmonary macrophages, respectively, but viral susceptibility of the guinea pigs was not enhanced. Both strains of VZV could be isolated from bronchial washings up to 48 hours after i.b. instillation of cell-associated virus, but neither strain was isolated thereafter from cultures of bronchial washings or explanted lung tissues.

Destroyed patellar articular surfaces were replaced with a high molecular weight polyethylene prosthesis in two patients. The patellofemoral articulation of the femur consisted of eburnated bone in one case and degenerative cartilage in the other. Both operations failed within one year because of a giant cell synovitis caused by a high volume (0.2 cc) of fine polyethylene (1-100 mu) wear particles. Ultra high molecular weight polyethylene should not be used as a prosthetic bearing surface to articulate against cortical, cancellous or eburnated bone or against degenerative articular cartilage in a major joint.

A Mo0.75Re0.25 alloy endplate was tested on a Nb TE011 mode microwave cavity resonant at 11.2 GHz. An upper bound for the surface resistance of 2.8 μΩ and a lower bound of 102 G for the microwave magnetic breakdown field were established for the alloy plate. Comparison of these results to current requirements for a superconducting linear accelerator demonstrated the potential feasibility of this alloy as a practical alternative to Nb and Pb for accelerator applications. This is the first alloy shown to be a potential alternative to Nb and Pb and arguments are presented which indicate possible practical advantages of Mo0.75Re0.25 over Nb and Pb.

Because of the increasing use of dissimilar metal combinations in the human body, we undertook an in vitro study to determine the compatibility and tendency to accelerate crevice corrosion of galvanic couples of cobalt-chromium alloy with either titanium, titanium alloy, or stainless steel. We employed an electrochemical open-circuit potential measurement test and a potentiostatic passive film-corrosion measurement test. The results demonstrated that the chromium alloy/stainless-steel couple was unstable. The cobalt-chromium alloy/titanium alloy couple was stable. Clinical Relevance: Cobalt-chromium alloys should not be used in combination with stainless steel but may be used in combination with titanium alloy. All usage of metal couples should be approached with the utmost caution.

The resistive critical field of severely drawn Nb increases far beyond the predictions of the GLAG theory for a homogeneous type‐II superconductor and becomes anisotropic. Although no model fits the situation exactly, nucleation of superconductivity at dislocation cell walls is a possible explanation.

The dependence of the anisotropy of the resistive critical field of severely deformed Nb on plastic strain and temperature, the anomalously large stress dependence, and the existence of resistive transitions in fields up to 48 kG all confirm the role of the dislocation cell wall in giving rise to critical‐field enhancement in this material.

Threshold estimates from multiple‐interval forced‐choice staircase procedures were studied using computer simulations. Two frequently cited psychometric function shapes, those for the signal known exactly and for high uncertainty, governed the hypothetical subject's responses in the simulations. Threshold estimates based on 100 trials were obtained for both psychometric functions, for three different stimulus change values, and for decision rules that estimated 70.7% and 79.4% correct levels. A total of 1000 replications in each condition were run. Each threshold estimate was calculated by averaging the stimulus levels at which a reversal in stimulus direction change occurred. For many of the simulated conditions, three‐alternative forced choice was the most efficient procedure (i.e., the variability of the estimates per unit of collection time was smallest). The validity of the simulations was tested using human performance data. [Work supported by NINCDS and IBM.]

The critical currents and ductilities of alloys containing 25 at. % Zr; 2, 5, or 10 at.% Ta; and the balance of Nb are determined. The effects of processing variables (such as cold-swaging) on the superconducting properties are noted. Specimens containing 5 at.% Ta are found to have critical currents greater than 10 amp and critical current densities greater than 10/sup 4/ amp/cm/ sup 2/ for magnetic fields in excess of 90 kOe. (T.F.H.)